This invention relates to an interferometer and more particularly to a compact three-beam interferometer.
Heretofore interferometers have been made with various different optical-detector arrangements. Three-beam interferometers have been set forth in the prior art in U.S. Pat. No. 3,487,227 in which three collinear apertures were placed in front of a lens producing an interference fringe pattern in the focal plane of the lens from monochromatic light passing through the three apertures. Another three-beam interferometer has been set forth in an article "Three Beam Interferometer for the Observation of Kinetic Cooling in Air", by L. Sica; Applied Optics, Vol. 12, pages 2848-2854, December 1973.
In the patented device, relative longitudinal vibration of the lens and detector slit cause optical path changes; i.e., noise in the center beam relative to the edge beams which appears along with the signal output. In the device of the published article, longitudinal vibrations are also confused with the output signal.